LAUSANNE, March 30. /TASS/. As talks between world powers and Tehran have intensified in Lausanne, Switzerland, it is still unclear whether the sides would be able to reach a political deal on Iran’s nuclear program, a source in Iran’s delegation told TASS.

After a lengthy round of consultations between the P5+1 (the five permanent members of the UN Security Council - the United States, Russia, China, the United Kingdom, and France plus Germany) and Tehran on Sunday, there are still some key sticking points that remain unresolved.

Speaking on the outcome of the night discussions, the diplomatic source said "it is unclear whether Iran and the six world powers could reach a document on the political understanding in the coming days."

"There are differences and in some aspects they are significant," the source told TASS. "That’s why only the new day of negotiations and the meeting of the foreign ministers of six powers and Iran will show whether we will achieve the result," he said.

"We are ready to continue work and discuss the possible options. But only the forthcoming hours spent in the meeting rooms can show what will come out of this," the source added.

Under the agreement in late November 2014 in Vienna, the sides are expected to reach an understanding on the ways out of the crisis on Iran’s nuclear dossier by the end of March.

The foreign ministers from the six powers are searching for a compromise and do not set the task of reaching a final deal to be signed. The highest goal is to have a comprehensive political declaration defining the key principles of the future deal.

The negotiations approached a critical point on Sunday as all the participating foreign ministers arrived in Lausanne.

Iran's deputy foreign minister, Abbas Araqchi, said: "The intense talks are ongoing, and two or three points at issue remain," in particular mentioning the sanctions problem. "Iran insists on lifting all the UN Security Council resolutions as part of reaching the agreement," he said.

As for the international sanctions, the unilateral punitive measures of the Western countries are not being discussed at these talks, but in fact their step-by-step lifting will be tied to the lifting the UN sanctions. The sides have yet failed to agree on the conditions and timeframe for the move.

Another controversial issue is the problem of centrifuges in Iran for uranium enrichment. Iran has some 19,000 of them. The Western diplomats insist that this number should be cut by one third.

There is also no agreement on how long the restrictions on nuclear research in Iran will last. Tehran wants to resume the research in full after the expiration of the final deal that is expected to be signed for 10 years, while the six powers do not agree to this.

The main stumbling block is the regime of checks that are due to be carried out by the International Atomic Energy Agency (IAEA) inspectors. The organization is not taking part in the talks in Switzerland but is ready to play an active role in controlling the implementation of a possible agreement.